The best tip is to start writing now, as soon as you start the research. Do not wait until after you have some data.
The thesis is the only thing examined for a PhD, and sometimes for an MSc. It does not matter how much lab and field work you did. Nor how many wonderful experiences, disasters or fun you had along the way. All the examiners can consider is the thesis.
If doing a PhD, start publishing in peer-reviewed journals asap. Getting your work published is an essential part of professional training and provides independent feedback on your work, and strengthens your CV.
Use your supervisor(s) for advice on the science of the thesis. Give them high-quality drafts. Otherwise, they will waste time correcting editorial matters, like the writing and presentation. This can distract them from focusing on what is really important. The science includes the overall structure, flow of ‘arguments’, aims, methods, analysis, how to present the results (graphs, tables, diagrams), what they mean, and how to frame and articulate the findings. Note that supervisors have an ethical responsibility to help you learn, and should not help you too much by doing your work for you.
Conflicting advice is good! If you are lucky to have several advisors, use them. Consult with other experts as needed. Indeed, your supervisor(s) may help with introductions to other experts, and it is good to keep them informed of such cooperation. If advisors views vary, this is a great way to learn more. The more contradictory the better; it enables you to understand their context, thinking, and ultimately how science advances, and to find your own viewpoint.
How much help can you get? The University of Auckland recommends each graduate student gets 50 hours of advisor time per year, including time for administration, practical training, meetings, and commenting on drafts. Some departments suggest supervisors should only read one or two drafts of an MSc thesis, and be given two weeks to review drafts.
For tips on writing see here.
A common shortfall of MSc theses is that because of their hard deadline, the last and most important section, the Discussion, is often given the least amount of time. I have seen many MSc with an excellent Introduction, Methods and good Results, but a poorly written Discussion. I know how this happens and expect it will happen again. But it is avoidable. Aim to finish your thesis a month or two early and spend that time fine-tuning the presentation, and especially the final discussion.
For supervisors and graduate students see the Doctoral Writing blogs.
One of the University of Auckland Professors provides some tools to help improve your writing at The Writer’s Diet.
Very helpful advice on how to phrase text, from introductory statements to conclusions, comparing and explaining, and more: Academic Phrasebank provides